Current Biology
Volume 30, Issue 9, 4 May 2020, Pages 1664-1671.e2
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Article
Sleep Time in the European Starling Is Strongly Affected by Night Length and Moon Phase

https://doi.org/10.1016/j.cub.2020.02.052Get rights and content
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Highlights

  • Starlings display strong phenotypical variation in sleep-wake regulation

  • Full moon reduces sleep time in starlings with about 2 h

  • Starlings sleep 5 h less per day during summer compared to winter

  • Starlings have more mid-day naps and higher sleep pressure in summer

Summary

Sleep is considered to be of crucial importance for performance and health, yet much of what we know about sleep is based on studies in a few mammalian model species under strictly controlled laboratory conditions. Data on sleep in different species under more natural conditions may yield new insights in the regulation and functions of sleep. We therefore performed a study with miniature electroencephalogram (EEG) data loggers in starlings under semi-natural conditions, group housed in a large outdoor enclosure with natural temperature and light. The birds showed a striking 5-h difference in the daily amount of non-rapid-eye-movement (NREM) sleep between winter and summer. This variation in the amount of NREM sleep was best explained by night length. Most sleep occurred during the night, but when summer nights became short, the animals displayed mid-day naps. The decay of NREM sleep spectral power in the slow-wave range (1.1–4.3 Hz) was steeper in the short nights than in the longer nights, which suggests that birds in summer have higher sleep pressure. Additionally, sleep was affected by moon phase, with 2 h of NREM sleep less during full moon. The starlings displayed very little rapid-eye-movement (REM) sleep, adding up to 1.3% of total sleep time. In conclusion, this study demonstrates a pronounced phenotypical flexibility in sleep in starlings under semi-natural conditions and shows that environmental factors have a major impact on the organization of sleep and wakefulness.

Keywords

avian sleep
REM sleep
sleep homeostasis
sleep restriction
annual cycle
seasonal rhythm
photoperiod
moon phase
light
songbird

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These authors contributed equally

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